No one is quite sure of the origins of these idyllic natural hot springs at an abandoned mountain resort.

The ruins of a medieval castle linked to the murderous French lord that inspired the famous legend of Bluebeard.

A well-restored ancient archaeology site gives a real feel for life during the Roman age.

England's most notorious suicide spot.

These stark white cliffs were spat up by the sea and are slowly being retaken by it.

Henry VIII's forgotten castle was built by the gunpowder-obsessed king to be defended solely by cannons.

The ruins of an ancient stadium that hosted gripping chariot and horse races.

The alleged birthplace of Lady Jane Grey, who was executed at age 16 for claiming the throne of England.

One of its engravings is believed to be among the first representations of medical and surgical instruments.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.

Dramatic river bend surrounds a natural red-rocked pedestal.

Most-visited and most-photographed slot canyon in the American Southwest.

A well-preserved Ancestral Puebloan ruin tucked beneath a desert cliff.

Ancestral Puebloan ruins, natural arches, and box canyons abound in this seldom-visited corner of Monument Valley Navajo Tribal Park.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

This unique historical monument features large concrete spheres designed to resemble fallen stars.

A diminutive plaque recalls the treetop sniper who almost killed Abe Lincoln.

The fountains of the U.S. Navy Memorial are annually salted with water from the Seven Seas as part of a nautical ritual.

A cylinder monument with a spectacular vista commemorates a friendship that some say never existed.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

The granddaddy of English geoglyphs dates back to the late Bronze Age.

65 million-year-old chalk outcroppings mark the end of the Jurassic Coast.

These ancient sunken lanes were naturally tunneled into the soft ground by countless footsteps.